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Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around (Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pangaea, drifting further north after the split and finally broke apart with the opening of the North Atlantic Ocean 56 Mya. The name is a Blend word of Laurentia and Eurasia.
Laurentia, Avalonia, Baltica, and a series of smaller , collided in the Caledonian orogeny c. 400 Mya to form Laurussia. Laurussia then collided with Gondwana to form Pangaea. Kazakhstania and Siberia were then added to Pangaea 290–300 Mya to form Laurasia. Laurasia finally became an independent continental mass when Pangaea broke up into Gondwana and Laurasia.
In 1904–1909, Austrian geologist Eduard Suess proposed that the continents in the Southern Hemisphere were once merged into a larger continent called Gondwana. In 1915, German meteorologist Alfred Wegener proposed the existence of a supercontinent that he called Pangaea. In 1937, South African geologist Alexander du Toit proposed that Pangaea was divided into two larger landmasses, Laurasia in the Northern Hemisphere and Gondwana in the Southern Hemisphere, separated by the Tethys Ocean.
"Laurussia" was defined by Swiss geologist Peter Ziegler in 1988 as the merger between Laurentia and Baltica along the northern Caledonian suture. The "Old Red Continent" is an informal name often used for the Silurian-Carboniferous deposits in the central landmass of Laurussia.
Several earlier supercontinents proposed and debated in the 1990s and later (e.g. Rodinia, Nuna, Nena) included earlier connections between Laurentia, Baltica, Siberia. These original connections apparently survived through one and possibly even two , though their intermittent duration and recurrent fit is debated.
Additional Proterozoic crust was accreted 1,800–1,300 Mya, especially along the Laurentia-Greenland-Baltica margin. Laurentia and Baltica formed a coherent continental mass with southern Greenland and Labrador adjacent to the Arctic margin of Baltica. A magmatic arc extended from Laurentia through southern Greenland to northern Baltica. The breakup of Columbia began 1,600 Mya, including along the western margin of Laurentia and northern margin of Baltica (modern coordinates), and was completed c. 1,300–1,200 Mya, a period during which mafic were emplaced, including MacKenzie and Sudbury in Laurentia.
Traces left by large igneous provinces provide evidences for continental mergers during this period. Those related to Proto-Laurasia includes:
Siberia was located near but at some distance from Laurentia's northern margin in most reconstructions. In the reconstruction of some Russian geologists, however, the southern margin (modern coordinates) of Siberia merged with the northern margin of Laurentia, and these two continents broke up along what is now the -long Central Asian Foldbelt no later than 570 Mya and traces of this breakup can still be found in the Franklin dike swarm in northern Canada and the Aldan Shield in Siberia.
The Panthalassa opened and Rodinia began to breakup during the Neoproterozoic (c. 750–600 Mya) as Australia-Antarctica (East Gondwana) rifted from the western margin of Laurentia, while the rest of Rodinia (West Gondwana and Laurasia) rotated clockwise and drifted south. Earth subsequently underwent a series of glaciations – the Cryogenian (c. 650 Mya, also known as Snowball Earth) and the Rapitan and Ice Brook glaciations (c. 610–590 Mya) – both Laurentia and Baltica were located south of 30°S, with the South Pole located in eastern Baltica, and glacial deposits from this period have been found in Laurentia and Baltica but not in Siberia.
A mantle plume (the Central Iapetus Magmatic Province) forced Laurentia and Baltica to separate ca. 650–600 Mya and the Iapetus Ocean opened between them. Laurentia then began to move quickly () north towards the Equator where it got stuck over a cold spot in the Proto-Pacific. Baltica remained near Gondwana in southern latitudes into the Ordovician.
Pannotia broke apart in the late Precambrian into Laurentia, Baltica, Siberia, Gondwana. A series of continental blocks, the Cadomian, Avalonian, Cathaysian, Cimmerian terranes, broke away from Gondwana and began to drift north.
Avalonia rifted from Gondwana in the Early Ordovician and collided with Baltica near the Ordovician–Silurian boundary (480–420 Mya). Baltica-Avalonia was then rotated and pushed north towards Laurentia. The collision between these continents closed the Iapetus Ocean and formed Laurussia, also known as Euramerica. Another historical term for this continent is the Old Red Continent or Old Red Sandstone Continent, in reference to abundant red beds of the Old Red Sandstone during the Devonian. The continent covered including several large Arctic continental blocks.
With the Caledonian orogeny completed Laurussia was delimited thus:
During the Devonian (416–359 Mya) the combined landmass of Baltica and Avalonia rotated around Laurentia, which remained static near the Equator. The Laurentian warm, shallow seas and on shelves a diverse assemblage of benthos evolved, including the largest exceeding . The Old Red Sandstone Continent stretched across northern Laurentia and into Avalonia and Baltica but for most of the Devonian a narrow seaway formed a barrier where the North Atlantic would later open. Tetrapods evolved from fish in the Late Devonian, with the oldest known fossils from Greenland. Low sea-levels during the Early Devonian produced natural barriers in Laurussia which resulted in provincialism within the benthic fauna. In Laurentia the Transcontinental Arch divided into two provinces, with one of them confined to a large embayment west of the Appalachians. By the Middle Devonian, these two provinces had been united into one and the closure of the Rheic Ocean finally united faunas across Laurussia. High plankton productivity from the Devonian-Carboniferous boundary resulted in that left Shale in the basins of Laurentia.
Pangaea was completely assembled by the Permian except for the Asian blocks. The supercontinent was centred on the Equator during the Triassic and Jurassic, a period that saw the emergence of the Pangaean megamonsoon. Heavy rainfall resulted in high groundwater tables, in turn resulting in peat formation and extensive coal deposits.
During the Cambrian and Early Ordovician, when wide oceans separated all major continents, only pelagic marine organisms, such as plankton, could move freely across the open ocean and therefore the oceanic gaps between continents are easily detected in the fossil records of marine bottom dwellers and non-marine species. By the Late Ordovician, when continents were pushed closer together closing the oceanic gaps, benthos (brachiopods and trilobites) could spread between continents while and fishes remained isolated. As Laurussia formed during the Devonian and Pangaea formed, fish species in both Laurussia and Gondwana began to migrate between continents and before the end of the Devonian similar species were found on both sides of what remained of the Variscan barrier.
The oldest tree fossils are from the Middle Devonian pteridophyte Gilboa Fossil Forest in central Laurussia (today New York City, United States). In the late Carboniferous, Laurussia was centred on the Equator and covered by tropical rainforests, commonly referred to as the coal forest. By the Permian, the climate had become arid and these Carboniferous rainforests collapsed, Lycopodiopsida (giant mosses) were replaced by Cyatheales. In the dry climate a Detritivore fauna – including Annelid, Mollusca, and some Arthropod – evolved and diversified, alongside other arthropods who were herbivorous and carnivorous, and tetrapods – and such as Amphibian and early .
The Palaezoic-Mesozoic transition was marked by the reorganisation of Earth's tectonic plates which resulted in the assembly of Pangaea, and eventually its break-up. Caused by the detachment of subducted mantle slabs, this reorganisation resulted in rising that produced large igneous provinces when they reached the crust. This tectonic activity also resulted in the Permian–Triassic extinction event. Tentional stresses across Eurasia developed into a large system of rift basins (Urengoy, East Uralian-Turgay, Khudosey) and in the West Siberian Basin, the Pechora Basin, South China.
Laurasia and Gondwana were equal in size but had distinct geological histories. Gondwana was assembled before the formation of Pangaea, but the assembly of Laurasia occurred during and after the formation of the supercontinent. These differences resulted in different patterns of basin formation and transport of sediments. East Antarctica was the highest ground within Pangaea and produced sediments that were transported across eastern Gondwana but never reached Laurasia. During the Palaeozoic, c. 30–40% of Laurasia was covered by shallow marine water but only 10–20% of Gondwana was covered by shallow marine water.
The break-up of Rodinia also resulted in the opening of the long-lived Paleo-Asian Ocean between Baltica and Siberia in the north and Tarim and North China in the south. The closure of this ocean is preserved in the Central Asian Orogenic Belt, the largest orogen on Earth.
North China, South China, Indochina, Tarim broke off from Gondwana during the Silurian to Devonian periods; as the Paleo-Tethys Ocean opened behind them. Sibumasu and Qiantang and other Cimmerian continental fragments broke off in the Early Permian. Lhasa terrane, Burma terrane, Sikuleh, southwest Sumatra, West Sulawesi, and parts of Borneo, broke off during the Late Triassic-Late Jurassic.
During the Carboniferous and Permian, Baltica first collided with Kazakhstania and Siberia, then North China with Mongolia and Siberia. By the middle Carboniferous, however, South China had already been in contact with North China long enough to allow floral exchange between the two continents. The Cimmerian blocks rifted from Gondwana in the Late Carboniferous.
In the early Permian, the Neo-Tethys Ocean opened behind the Cimmerian terranes (Sibumasu, Qiantang, Lhasa) and, in the late Carboniferous, the Paleo-Tethys Ocean closed in front. The eastern branch of the Paleo-Tethys Ocean, however, remained opened while Siberia was added to Laurussia and Gondwana collided with Laurasia.
When the eastern Palaeo-Tethys closed 250–230 Mya, a series of Asian blocks – Sibumasu, Indochina, South China, Qiantang, Lhasa – formed a separate southern Asian continent. This continent collided 240–220 Mya with a northern continent – North China, Qinling, Qilian, Qaidam, Alex, Tarim – along the Central China orogen to form a combined East Asian continent. The northern margins of the northern continent collided with Baltica and Siberia 310–250 Ma, and thus the formation of the East Asian continent marked Pangaea at its greatest extent. By this time, the rifting of western Pangaea had already begun.
Pinaceae evolved in the early Mesozoic c. 250 Mya and the pine genus originated in Laurasia in the Early Cretaceous c. 130 Mya in competition with faster growing Flowering plant. Pines adapted to cold and arid climates in environments where the growing season was shorter or wildfire common; this evolution limited pine range to between 31° and 50° north and resulted in a split into two subgenera: Strobus adapted to stressful environments and Pine to fire-prone landscapes. By the end of the Cretaceous, pines were established across Laurasia, from North America to East Asia.
From the Triassic to the Early Jurassic, before the break-up of Pangaea, (crurotarsans, pterosaurs and dinosaurs including birds) had a global distribution, especially crurotarsans, the group ancestral to the Crocodilia. This cosmopolitanism ended as Gondwana fragmented and Laurasia was assembled. Pterosaur diversity reach a maximum in the Late Jurassic—Early Cretaceous and plate tectonic didn't affect the distribution of these flying reptiles. Crocodilian ancestors also diversified during the Early Cretaceous but were divided into Laurasian and Gondwanan populations; true crocodilians evolved from the former. The distribution of the three major groups of – the Sauropoda, Theropoda, and – was similar to that of the crocodilians. East Asia remained isolated with endemic species including Psittacosaurus (horned dinosaurs) and Ankylosauridae (club-tailed, armoured dinosaurs).
Meanwhile, Mammal slowly settled in Laurasia from Gondwana in the Triassic, the latter of which was the living area of their Permian Therapsida. They split in two groups, with australosphenida returning to Gondwana (and stayed there after Pangaea split) while Tribosphenida staying in Laurasia (until further descendants switched to Gondwana starting from the Jurassic).
In the early Eocene, a peak in global warming led to a pan-Arctic fauna with alligators and amphibians present north of the Arctic Circle. In the early Paleogene, landbridges still connected continents, allowing land animals to migrate between them. On the other hand, submerged areas occasionally divided continents: the Turgai Strait separated Europe and Asia from the Middle Jurassic to the Oligocene and as this strait dried out, a massive faunal interchange took place and the resulting extinction event in Europe is known as the Grande Coupure.
The Coraciiformes (an order of birds including kingfishers) evolved in Laurasia. While this group now has a mostly tropical distribution, they originated in the Arctic in the late Eocene c. 35 Mya from where they diversified across Laurasia and further south across the Equator.
The placental mammal group of Laurasiatheria is named after Laurasia.
By c. 83 Mya spreading had begun in the North Atlantic between the Rockall Basin, a continental fragment sitting on top of the Eurasian Plate, and North America. By 56 Mya, Greenland had become an independent plate, separated from North America by the Labrador Sea-Baffin Bay Rift. By 33 Mya, spreading had ceased in the Labrador Sea and relocated to the Mid-Atlantic Ridge. The opening of the North Atlantic Ocean had effectively broken Laurasia in two.
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